DE102018100373B4 - Process for vertical keystone correction in projection systems for head-up displays, laser projection devices and vehicles - Google Patents

Abstract

Method for projecting an image onto a surface (32), wherein at least one modulated projection laser (24) periodically with a first deflection frequency and a first deflection amplitude along a first axis (14) and with a second deflection frequency and a second deflection amplitude along a second axis (16 ) is deflected, wherein the second axis (16) is different from the first axis (14), and wherein the periodic deflection along the first axis (14) and / or second axis (16) with a modulation frequency and a modulation amplitude to compensate for a Distortion of the image is frequency-modulated, the modulation frequency being set to zero in a setting-up step, a distortion of the image being recorded, and the modulation frequency and / or modulation amplitude being calculated to compensate for the recorded distortion and being applied to the first and / or second deflection frequency.

Description

The invention relates to a method for projecting an image onto a surface, in particular provided by a windshield of a vehicle, a laser projection device which is set up to carry out such a method, and a vehicle with such a laser projection device.

Laser projection devices are well known. They use projection lasers with modulated intensity in the elementary colors, which are periodically deflected by mirror systems. So-called MEMS (Micro-ElectroMechanical Systems) mirrors are usually used for this purpose. These are micromirrors that can vibrate at high frequencies, for example with the help of piezoelectric drivers.

If the projection axis of such a laser projection device is not orthogonal to the projection surface, the resulting image will be distorted. If the projection axis is inclined towards the surface, for example, the image will be trapezoidal distortion, known as keystone distortion. Furthermore, distortions can be attributed to curved surfaces used as projection surfaces, for example the windshield of a vehicle, which is particularly problematic for head-up devices (HUD), which are used to project information onto the windshield.

It is known to compensate for such a distortion by using certain optics, for example lens systems. Another possibility for compensating for distortions is to calculate a pre-distortion for the projected image, so that an undistorted projection results. Both methods are comparatively complicated and cannot be easily adapted to changing projection conditions.

WO 2011/007 386 A2 discloses a correction method for laser scan projectors by varying the scan amplitude, which requires a complicated drive system for the MEMS mirrors that must be able to respond to rapid changes in the oscillation modes of the piezo drivers.

US 2014/0078121 A1 discloses an image display device comprising a light source that emits a laser beam, a scanning mirror that projects an image by scanning the laser beam vertically and horizontally by panning, and a scanning control section that relatively large the horizontal scanning amplitude of the scanning mirror on the side of a projection image with a reduced length compared to the horizontal scanning amplitude of the scanning mirror on the side of the projection image with an enlarged length in relation to distortion, the length of the top of the projection image and the length of the bottom of the projection image being different from each other.

U.S. 6,140,979 A discloses a display device comprising an image source that scans about two axes. In order to compensate for the movement about a first of the axes while oscillating about the second axis, the device includes a structure for generating a compensating movement about the first axis at a sampling rate which is equal to twice the sampling rate about the second axis. The offset scan can be a ramp or some other movement. The compensatory movement can be generated by an auxiliary scanner, such as a mechanical scanner, a piezoelectric scanner, a MEMS scanner or another scanner. Since the offset movement is very small, the additional scanner can work with a very small scanning angle.

US 2013/0120819 A1 discloses a scanning beam projection system comprising a scanning mirror having a fast scan axis and a slow scan axis. Movement on the fast scan axis is controlled by a fast scan mirror control system. The control system receives position information describing the angular displacement of the mirror. A fast scan drive signal is generated which causes the scan mirror to vibrate at a resonant frequency with a different amplitude.

The technical problem on which the present invention is based thus consists in specifying a method and a laser projection device which enable distortions to be corrected quickly, easily and flexibly. Another object of the present invention is to specify a vehicle with such a laser projection device.

This object is achieved by a method according to claim 1, a laser projection device according to claim 11, and a vehicle according to claim 14.

In a method for projecting an image onto a surface, in particular onto a windshield of a vehicle, according to the invention at least one modulated projection laser is periodically with a first deflection frequency and a first deflection amplitude along a first axis and with a second deflection frequency and a second deflection amplitude along a second axis deflected, the second axis being different from the first axis, in particular orthogonally to this, and wherein the periodic deflection is modulated along the first and / or second axis with a modulation frequency and a modulation amplitude to compensate for a distortion of the image.

By providing a frequency and / or amplitude modulation by superimposing a modulation oscillation in the above-mentioned manner, a particularly simple method is provided. This makes it possible, for example, to drive a MEMS mirror with two conventional piezo drivers for the first and second deflection oscillation, and to use a third driver to provide the modulation oscillation. In this way, no particularly high-precision piezo drivers have to be used for the device used with the above method.

Here, in a setup step, the modulation frequency is set to zero, a distortion of the image is recorded, and the modulation frequency and / or modulation amplitude is calculated to compensate for the recorded distortion and applied to the first and / or second deflection frequency. In other words, a distorted image is generated and recorded during the setup step and used as a basis for determining correction factors. This is particularly flexible since it enables the projection to be adapted to changing geometric conditions, in particular to changing projection surfaces.

In a further preferred embodiment of the invention, the first axis is a horizontal axis of the projected image and the second axis is a vertical axis of the projected image.

This enables a particularly simple driver program, since the path of the projection laser corresponds directly to the vertical and horizontal coordinates of the source image and the projection surface.

In a further preferred embodiment of the invention, the modulation frequency for the second axis is synchronized with the deflection frequency for the first axis.

In this way, the vertical extension of the projected image can be modulated as a function of the horizontal position. This allows for easy and immediate compensation for keystone distortion and can also be used to correct distortion caused by curved surfaces such as windshields.

was zu einer maximalen Winkelabweichung gegenüber der nicht-modulierten Umlenkung von $$\vartheta =\frac{{\theta }_v-\alpha }{2}$$

führt, wobei θh den Winkel des horizontalen Sichtfelds der Projektion bezeichnet, θv den Winkel des vertikalen Sichtfelds der Projektion bezeichnet, δh den horizontalen Kippwinkel der Verzerrung bezeichnet, δv den vertikalen Kippwinkel der Verzerrung bezeichnet, α den Gesamtmaximalausgleichswinkel bezeichnet, und ϑ die maximale Ausgleichswinkelabweichung bezeichnet.In a further preferred embodiment of the invention, by applying the modulation to the deflection along the second axis, the second deflection amplitude is modulated by a maximum angle $$\alpha =atan\left\{\frac{\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)+\text{tan}\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="\theta \; v"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_v}{2}+{\delta }_v\right)\right]\times \text{cos}\left(\frac{{\theta }_{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">H</figure-callout>}}}{2}+{\delta }_H\right)\times \text{cos}\left(\frac{{\theta }_H}{2}-{\delta }_H\right)}{\text{cos}\left(\frac{{\theta }_H}{2}-{\delta }_H\right)-\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)\times \text{tan}\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="\theta \; v"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_v}{2}+{\delta }_v\right)\times {\text{cos}}^2\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="\theta \; H"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_H}{2}+{\delta }_H\right)\right]}\right\}$$

resulting in a maximum angular deviation compared to the non-modulated deflection of $$\vartheta =\frac{{\theta }_v-\mathrm{<figure-callout\; id="2"\; label="\alpha "\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\alpha </figure-callout>}}{2}$$

leads, where θh denotes the angle of the horizontal field of view of the projection, θv denotes the angle of the vertical field of view of the projection, δh denotes the horizontal tilt angle of the distortion, δv denotes the vertical tilt angle of the distortion, α denotes the total maximum compensation angle, and ϑ denotes the maximum compensation angle deviation.

The mathematical relationships presented above provide a direct relationship between the projection geometry and the amplitude modulation required to compensate for the distortion. It is particularly noteworthy that the modulation frequency and amplitude to compensate for the distortion is a constant function so that the modulation driver of the MEMS device used for projection is not required to make rapid changes in its vibrational settings.

und die Wellenform für die periodische Modulation entlang der zweiten Achse ist gegeben durch: $$y_{comp}=v_{init}+\frac{\alpha }{2}\text{cos}\left(2\mathrm{\pi }\frac{f_r}{2}\right)$$

wobei der anfängliche Ausgleich $$v_{init}=-\frac{2{\delta }_v\vartheta }{{\theta }_v}$$

beträgt.In a further preferred embodiment of the invention, the waveform for the periodic deflection along the second axis is given by: $$y_{OriGinal}=\frac{{\mathrm{<figure-callout\; id="2"\; label="\theta \; v"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_v}{2}\text{cos}\left(2\mathrm{\pi }\frac{f_r}{2}\right)$$

and the waveform for periodic modulation along the second axis is given by: $$y_{cOmp}=v_{init}+\frac{\mathrm{<figure-callout\; id="2"\; label="\alpha "\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\alpha </figure-callout>}}{2}\text{cos}\left(2\mathrm{\pi }\frac{f_r}{2}\right)$$

being the initial balance $$v_{init}=-\frac{2{\delta }_v\vartheta }{{\theta }_v}$$

amounts to.

In the equations above, denotes the repetition frequency of the projection. Like the modulation parameters mentioned above, the waveform for the periodic deflection along the second axis is an immutable function, so that the piezo driver for the second axis and the piezo driver for the modulation can each be controlled by constant, unchanging parameters.

In a further preferred embodiment of the invention, the surface onto which the image is projected is curved.

This makes it possible to use the above-described method for projecting onto surfaces such as windshields of vehicles, for example for use as a head-up device in order to provide a driver with information directly on the windshield that relates to his view of the surroundings Overlay vehicle.

In a further preferred embodiment of the invention, the modulation frequency and / or amplitude for the first and / or second axis is determined by calculating the point of intersection of a ray, which projects onto an imaginary plane tangential to the curved surface, with the curved surface.

This enables a simple geometric determination of the correction parameters that are required to provide a distortion-free image on a curved projection surface.

In a further preferred embodiment of the invention, the periodic deflection along the first axis and the second axis is provided by a MEMS mirror with two axes that correspond to the first and second axes, and a first actuator with the mirror along the first axis the first deflection frequency oscillates, and a second actuator oscillates the mirror along the second axis at the second deflection frequency, and at least one further actuator oscillates the first and / or second axis at the modulation frequency.

This enables the use of particularly simple and compact projection hardware, since known conventional MEMS mirror systems only need to be upgraded with an additional actuator in order to provide the required modulation, so that the overall size of the MEMS mirror system used for the projection remains largely unchanged.

In a further preferred embodiment of the invention, the periodic deflection along the first axis is provided by a first MEMS mirror, and the periodic deflection along the second axis is provided by a second MEMS mirror, and a first actuator along the first mirror first axis oscillates at the first deflection frequency, and a second actuator oscillates the second mirror along the second axis at the second deflection frequency, and at least one further actuator oscillates at least one further mirror along the first and / or second axis at the modulation frequency.

This alternative embodiment can be used to upgrade existing MEMS projection systems, since only the addition of a third mirror with an associated actuator is necessary.

The invention also relates to a laser projection device which is set up to carry out a method as described above, and to a vehicle with such a laser projection device which is preferably used as a head-up display projection device for projecting an image onto a windshield of the vehicle.

It is preferred that the first actuator comprises a piezo actuator, in particular an electrostatic actuator, and / or the second actuator comprises a piezo actuator, in particular an electromagnetic actuator, and / or the third actuator comprises a piezo actuator, in particular one electrostatic actuator.

In all of these cases, the advantages described above also apply.

• 1 eine schematische Darstellung eines MEMS-Spiegelsystems mit zwei Achsen und einem Spiegel zur Verwendung in einer ersten Ausführungsform der vorliegenden Erfindung;
• 2 eine schematische Darstellung eines MEMS-Spiegelsystems mit zwei Achsen und drei Spiegeln zur Verwendung in einer zweiten Ausführungsform der vorliegenden Erfindung;
• 3 eine schematische Darstellung des Strahlengangs eines MEMS-Projektionssystems über eine Projektionsoberfläche;
• 4 schematische Darstellungen von verschiedenen Verzerrungstypen während der Laserprojektion;
• 5 ein Ablaufdiagramm für ein Beispiel eines Verfahren gemäß der vorliegenden Erfindung;
• 6 schematische Darstellungen der Ausgleichsmodulation gemäß einer Ausführungsform der vorliegenden Erfindung;
• 7 eine schematische Ansicht der geometrischen Bedingungen während einer winkelversetzten Projektion;
• 8 schematische Ansichten der resultierenden Wellenformen der Modulationsspiegelbewegung gemäß einer Ausführungsform der vorliegenden Erfindung; und
• 9 eine schematische Ansicht der geometrischen Bedingungen während der Projektion auf eine gekrümmte Oberfläche.

The invention and its embodiments are described in detail below with reference to the drawings. The drawings show in:

• 1 a schematic representation of a MEMS mirror system with two axes and a mirror for use in a first embodiment of the present invention;
• 2 a schematic representation of a MEMS mirror system with two axes and three mirrors for use in a second embodiment of the present invention;
• 3 a schematic representation of the beam path of a MEMS projection system over a projection surface;
• 4th schematic representations of different types of distortion during laser projection;
• 5 a flow chart for an example of a method according to the present invention;
• 6th schematic representations of the equalization modulation according to an embodiment of the present invention;
• 7th a schematic view of the geometric conditions during an angularly offset projection;
• 8th schematic views of the resultant waveforms of modulating mirror movement according to an embodiment of the present invention; and
• 9 a schematic view of the geometric conditions during projection onto a curved surface.

As in 1 shown comprises a MEMS device 10 a mirror for a laser projection device 12th on that around a first axis 14th and a second axis 16 can be swung with the axes 14th , 16 are preferably orthogonal to one another. The oscillation around the first axis 14th is by a first actuator 18th driven, which can be a piezo actuator, in particular an electrostatic actuator. The oscillation around the second axis 16 is mainly through a second actuator 20th driven, which can also be a piezo actuator, in particular an electromagnetic actuator. About the oscillation around the second axis 16 to modulate is a third actuator 22nd on the second axis 16 arranged. The third actuator 22nd imparts a second oscillation function with which the first oscillation function generated by the second actuator 20th is provided, is overlaid to compensate for distortion in the projected image.

Alternatively, as in 2 shown, light that is generated by a laser 24, which can also have several laser sources in several colors, the intensity of which can be modulated as a function of time, is initially via a first mirror 26th reflected by a first actuator (not shown in the figure) about the first axis 14th can be swung. The reflected light is on a second mirror 28 steered around a first second axis 16 can be swung, and on to a third mirror 30th steered, which also oscillates around a second axis 16 suitable is. In this embodiment, the third mirror represents 30th the function of imparting a modulation oscillation to the oscillation prepared by the second mirror 28 is provided, again to compensate for distortions in the projected image.

As a result of the vibrations described above, the projected laser light crosses a projection surface 32 , as in 3 where the laser moves horizontally, that is, along the first axis, which is the X-axis, and is slowly moved in a vertical pattern, that is, along the second axis, which is the Y-axis.

• Um eine Bildwiederholungsrate von 60 Hz mit 1200 Zeilen zu erzielen, müssen die folgenden Bedingungen erfüllt sein:
  • - vertikale Achse (Y-Achse) schwingt 30 Hz (60 Hz/2) -> mit Periode = 33,333 ms
  • - horizontale Achse (X-Achse) schwingt 18 kHz (vertikale Auflösung * vertikale Schwingung /2)

A typical example is characterized in that:

• To achieve a refresh rate of 60 Hz with 1200 lines, the following conditions must be met:
  • - vertical axis (Y-axis) oscillates 30 Hz (60 Hz / 2) -> with period = 33.333 ms
  • - horizontal axis (X-axis) oscillates 18 kHz (vertical resolution * vertical oscillation / 2)

Therefore, the vertical axis is often referred to as the slow axis (due to the lower frequency vibration) while the horizontal axis is considered to be the fast axis.

The ideal projection geometry, as in 3 shown, can generally only be achieved if the projection axis is absolutely perpendicular to the projection surface 32 is. In many cases this cannot be achieved, resulting in distortion of the projected image 34 ' , 34 '' on the projection surface 32 leads, as in 4th shown. The same topic arises from the projection onto a non-flat surface, for example a windshield of a vehicle.

In order to compensate for such distortions, a method according to the invention and as shown in flowchart 5 can be used. After an initialization step S10 becomes the shape of a projected image given the geometric conditions in step S12 calculated. In the next step S14 it is checked whether the projected image is rectangular, i.e. free of distortion; and if this is not the case, in step S16 a distortion compensation, in particular a keystone compensation, is applied, whereas otherwise, if there is no distortion, the method goes directly to a subsequent step S18 transforms. In step S18 it is determined whether the aspect ratio of the image is the same as the initial setting; in other words, it is checked whether there are additional distortion effects. If this is not the case, a subsequent step checks S20 whether the vertical height of the resulting image is higher than it should be according to the image's initial aspect ratio. If so, vertical compensation is applied, which can be done by frequency modulating the third actuator 22nd ( 1 ) or the third Mirror 30th ( 2 ) is changed. In a further step S24 it is checked whether the horizontal length of the resulting image is longer than it should be according to the aspect ratio at the beginning. If this is the case, a further horizontal adjustment is made in step S26 applied. If all corrections are applied as desired, the method ends in step S28 , and a correctly sized, distortion-free image can be projected.

The details of the correction for distortion along the vertical axis with the embodiment 1 are in 6th shown. A function curve 36 shows the non-modulated oscillation of the mirror 12th along the second axis 16 , whereas the function curve 38 shows the modulation oscillation of the mirror 12th along the same axis. Since the compensation is synchronized with the horizontal axis movement, the total vertical deflection of the laser beam depends on the horizontal position. This can be trapezoidal distortion resulting from an oblique projection angle between the MEMS device 10 and the projection surface 32 and correct distortions resulting from projection onto a curved projection surface.

The geometric basis for this is in 6th shown. As can be seen, the compensation modulation oscillation has a total angular amplitude α , which results in a difference ϑ between the uncorrected oscillation and the modulation oscillation (i.e. maximum compensation amplitude), where θv is the total amplitude of the uncorrected oscillation of the mirror along the second axis 16 referred to (i.e. vertical field of view (FoV)).

Referring now to 7th : With the coordinates (x1, y1) indicating the upper left corner of the projected image, (x2, y2) indicating the upper right corner of the projected image, (x3, y3) indicating the lower left corner of the projected image and (x4, y4), which indicate the lower right corner of the projected image, can specify the required correction angles for the upper right and lower right corners by the angles β and γ are designated.

List of reference symbols

θ h

denotes the angle of the horizontal field of view of the projection,

θ v

denotes the angle of the vertical field of view of the projection,

δ h

denotes the horizontal tilt angle of the projected image,

δ v

denotes the vertical tilt angle of the projected image,

θ

denotes the maximum compensation amplitude,

α

denotes the total maximum compensation amplitude,

β

denotes the top, vertical, maximum compensation amplitude,

γ

denotes the underside, vertical maximum compensation amplitude,

d

refers to the distance between the MEMS device 10 and the projection surface 32 , and

x1 to x4

denote the boundary corners of the projected image on the X-axis, and

y1 to y4

denote the boundary corners of the projected image on the Y-axis.

Die vertikale Koordinate der oberen rechten Ecke folgt Gleichung (2): $$y2=\frac{d}{\text{cos}\left(\frac{\theta h}{2}-\delta h\right)\times \text{tan}\left(\frac{\theta v}{2}-\delta v\right)}$$

Dies führt auf Gleichung (3): $$\beta =\text{atan}\left\{\frac{\text{tan}\left(\frac{\theta v}{2}+\delta v\right)\times \text{cos}\left(\frac{\theta h}{2}+\delta h\right)}{\text{cos}\left(\frac{\theta h}{2}-\delta h\right)}\right\}+\delta v$$

Analog folgt Winkel γ Gleichung (4): $$\gamma =\text{atan}\left\{\frac{\text{tan}\left(\frac{\theta v}{2}-\delta v\right)\times \text{cos}\left(\frac{\theta h}{2}+\delta h\right)}{\text{cos}\left(\frac{\theta h}{2}-\delta h\right)}\right\}-\delta v$$

Da die benötigte Gesamtamplitude α der Summe der Winkel β und γ entspricht, folgt aus der allgemein bekannten Gleichung (5), die für alle u, v gilt: $$\text{atan }u+\text{atan }u=\frac{u+v}{1-uv}$$

dass gemäß Gleichung (6) $$\alpha =atan\left\{\frac{\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)+\text{tan}\left(\frac{{\theta }_v}{2}+{\delta }_v\right)\right]\times \text{cos}\left(\frac{{\theta }_h}{2}+{\delta }_h\right)\times \text{cos}\left(\frac{{\theta }_h}{2}-{\delta }_h\right)}{\text{cos}\left(\frac{{\theta }_h}{2}-{\delta }_h\right)-\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)\times \text{tan}\left(\frac{{\theta }_v}{2}+{\delta }_v\right)\times {\text{cos}}^2\left(\frac{{\theta }_h}{2}+{\delta }_h\right)\right]}\right\}$$

mit Gleichung (7) $$\vartheta =\frac{\theta v-\alpha }{2}$$

gilt.From the basic geometry of this projection it can be seen that the angle β the following equation (1) follows: $$\beta =\text{atan}\left(\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">y</figure-callout>}2\times \text{cos}\left(\frac{\theta \mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">H</figure-callout>}}{2}+\delta H\right)\times \frac{1}{d}\right)+\delta v$$

The vertical coordinate of the upper right corner follows equation (2): $$\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">y</figure-callout>}2=\frac{d}{\text{cos}\left(\frac{\theta H}{2}-\delta H\right)\times \text{tan}\left(\frac{\theta v}{2}-\delta v\right)}$$

This leads to equation (3): $$\beta =\text{atan}\left\{\frac{\text{tan}\left(\frac{\mathrm{<figure-callout\; id="2"\; label="\theta \; v"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\theta </figure-callout>}v}{2}+\delta v\right)\times \text{cos}\left(\frac{\theta \mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">H</figure-callout>}}{2}+\delta H\right)}{\text{cos}\left(\frac{\theta H}{2}-\delta H\right)}\right\}+\delta v$$

Analogously, the angle γ equation (4) follows: $$\gamma =\text{atan}\left\{\frac{\text{tan}\left(\frac{\theta v}{2}-\delta v\right)\times \text{cos}\left(\frac{\theta \mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">H</figure-callout>}}{2}+\delta H\right)}{\text{cos}\left(\frac{\theta H}{2}-\delta H\right)}\right\}-\delta v$$

Since the required total amplitude α the sum of the angles β and γ corresponds to, follows from the well-known equation (5), which applies to all u, v: $$\text{atan}u+\text{atan}u=\frac{u+v}{1-uv}$$

that according to equation (6) $$\alpha =atan\left\{\frac{\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)+\text{tan}\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="\theta \; v"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_v}{2}+{\delta }_v\right)\right]\times \text{cos}\left(\frac{{\theta }_{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">H</figure-callout>}}}{2}+{\delta }_H\right)\times \text{cos}\left(\frac{{\theta }_H}{2}-{\delta }_H\right)}{\text{cos}\left(\frac{{\theta }_H}{2}-{\delta }_H\right)-\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)\times \text{tan}\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="\theta \; v"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\theta </figure-callout>}}_v}{2}+{\delta }_v\right)\times {\text{cos}}^2\left(\frac{{\theta }_{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">H</figure-callout>}}}{2}+{\delta }_H\right)\right]}\right\}$$

with equation (7) $$\vartheta =\frac{\theta v-\mathrm{<figure-callout\; id="2"\; label="\alpha "\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">\alpha </figure-callout>}}{2}$$

applies.

• Durch Hinzuaddieren einer vertikalen, zweiten Schwingungsresonanzwellenform 39, die mit der horizontalen Schwingungsresonanz entsprechend der folgenden Gleichung (9) und wie in der Mitte von 8 dargestellt synchronisiert ist:
  • (a+b cos c) sin d
  • a = Verhältnis von (V Kippen und ½von V Scan-Winkel) zu maximalem Ausgleichswinkel
  • b = ½ des maximalen Ausgleichs
  • c = ½ der Bildwiderholungsrate
  • d = 2 c (1/2 v Auflösung) = c v Auflösung
  wird eine finale Wellenform 40 erhalten.

The original waveform as shown in function curve 36 and the compensation amplitude waveform as shown in function curve 38 can be determined according to equations (8) below:

• By adding a vertical second vibration resonance waveform 39 corresponding to the horizontal vibration resonance according to the following equation (9) and as in the middle of FIG 8th is synchronized:
  • (a + b cos c) sin d
  • a = ratio of (V tilt and ½ of V scan angle) to maximum compensation angle
  • b = ½ of the maximum compensation
  • c = ½ the frame rate
  • d = 2 c (1/2 v resolution) = cv resolution
  a final waveform 40 is obtained.

In the above examples, the compensation for a trapezoidal or keystone distortion that can be traced back to a non-orthogonal projection axis was shown. The same principle can be applied for projection onto curved surfaces, as in 9 shown. In this case, amplitude modulations must be applied to both axes and, if necessary, additional intensity modulations must be applied in order to provide a homogeneous or evenly bright display.

How out 9 As can be seen, the basic correction for a curved surface must be the geometric difference between the curved projection surface 32 and an imaginary projection plane 42.

Folglich kann die korrigierte X-Koordinate für die obere rechte Ecke des Bilds (als Punkt 1 in 9 dargestellt) aus der folgenden Gleichung (11) gewonnen werden: $$x_{corr}=\left(\frac{distance}{\text{cos}\left(\frac{V_{sweep}}{2}+Vtilt\right)}\right)\times \text{tan}\left(\frac{Hsweep}{2}+Htilt\right)$$

wohingegen die korrigierte X-Koordinate für die untere rechte Ecke des projizierten Bilds aus Gleichung (12) gewonnen werden kann: $$x_{corr}=\left(\frac{distance}{\text{cos}\left(\frac{V_{sweep}}{2}+Vtilt\right)}\right)\times \text{tan}\left(\frac{Hsweep}{2}+Htilt\right)$$

wobei Vsweep und Hsweep die vertikalen und horizontalen Sweep-Winkel und Vtilt und Htilt die vertikalen und horizontalen Kippkorrekturwinkel bezeichnen.The geometry of the curved surface along the Z axis in 9 is approximated in this example by a parabola, resulting in a deflection angle θ and a distance r in equation (10) leads to: $$z=\left(\frac{x\text{sin}\theta }{\text{cos}\theta }-\frac{x}{\text{sin}\theta }\right)=\left(r\text{sin}\theta \times \text{tan}\theta \right)-r$$

As a result, the corrected X coordinate for the upper right corner of the image (as point 1 in 9 can be obtained from the following equation (11): $$x_{cOrr}=\left(\frac{distance}{\text{cos}\left(\frac{V_{swee\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">p</figure-callout>}}}{2}+Vtilt\right)}\right)\times \text{tan}\left(\frac{Hswee\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">p</figure-callout>}}{2}+Htilt\right)$$

whereas the corrected X coordinate for the lower right corner of the projected image can be obtained from equation (12): $$x_{cOrr}=\left(\frac{distance}{\text{cos}\left(\frac{V_{swee\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">p</figure-callout>}}}{2}+Vtilt\right)}\right)\times \text{tan}\left(\frac{Hswee\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="DE102018100373B4\_0026.png"\; state="\{\{state\}\}">p</figure-callout>}}{2}+Htilt\right)$$

where Vsweep and Hsweep denote the vertical and horizontal sweep angles and Vtilt and Htilt denote the vertical and horizontal tilt correction angles.

In this way a completely undistorted image can be provided on any curved surface which can conveniently be approximated as a parabola.

In summary, by means of the invention, a method and a device are provided which enable projection geometries to be easily adapted to changing projection angles and changing geometries of the projection surface.

Claims (15)

Method for projecting an image onto a surface (32), wherein at least one modulated projection laser (24) periodically with a first deflection frequency and a first deflection amplitude along a first axis (14) and with a second deflection frequency and a second deflection amplitude along a second axis (16 ) is deflected, wherein the second axis (16) is different from the first axis (14), and wherein the periodic Deflection along the first axis (14) and / or second axis (16) is frequency-modulated with a modulation frequency and a modulation amplitude to compensate for a distortion of the image, the modulation frequency being set to zero in a setup step, a distortion of the image being recorded, and the modulation frequency and / or modulation amplitude is calculated to compensate for the recorded distortion and applied to the first and / or second deflection frequency. Procedure according to Claim 1 wherein the second axis (16) is orthogonal to the first axis (14). Procedure according to Claim 1 or 2 wherein the first axis (14) is a horizontal axis of the projected image (34) and the second axis (16) is a vertical axis of the projected image. Procedure according to Claim 3 , wherein the modulation frequency for the second axis (16) is synchronized with the deflection frequency for the first axis (14). Procedure according to Claim 4 , whereby by applying the modulation to the deflection along the second axis (16) the second deflection amplitude by a total maximum compensation angle α: $$\alpha =atan\left\{\frac{\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)+\text{tan}\left(\frac{{\theta }_v}{2}+{\delta }_v\right)\right]\times \text{cos}\left(\frac{{\theta }_H}{2}+{\delta }_H\right)\times \text{cos}\left(\frac{{\theta }_H}{2}-{\delta }_H\right)}{\text{cos}\left(\frac{{\theta }_H}{2}-{\delta }_H\right)-\left[\text{tan}\left(\frac{{\theta }_v}{2}-{\delta }_v\right)\times \text{tan}\left(\frac{{\theta }_v}{2}+{\delta }_v\right)\times {\text{cos}}^2\left(\frac{{\theta }_H}{2}+{\delta }_H\right)\right]}\right\}$$

is modulated, resulting in a maximum angular deviation compared to the non-modulated deflection of $$\vartheta =\frac{{\theta }_v-\alpha }{2}$$

where θh denotes the angle of the horizontal field of view of the projection, θv denotes the angle of the vertical field of view of the projection, δh denotes the horizontal tilt angle of the distortion, and δv denotes the vertical tilt angle of the distortion. Procedure according to Claim 5 , wherein the waveform for the periodic deflection along the second axis (16) is given by $$y_{OriGinal}=\frac{{\theta }_v}{2}\text{cos}\left(2\pi \frac{f_r}{2}\right)$$

and the waveform for periodic modulation along the second axis is given by $$y_{cOmp}=v_{init}+\frac{\alpha }{2}\text{cos}\left(2\pi \frac{f_r}{2}\right)$$

being the initial balance $$v_{init}=\frac{2{\delta }_v\vartheta }{{\theta }_v}$$

is. A method as claimed in any preceding claim, wherein the surface (32) on which the image is projected is curved. Procedure according to Claim 7 , wherein the modulation frequency and / or amplitude for the first (14) and / or second axis (16) by calculating the intersection of a ray projecting onto a flat, imaginary plane (42) tangential to the curved surface (32), is determined with the curved surface (32). Method according to one of the preceding claims, wherein the periodic deflection along the first axis (14) and the second axis (16) by a MEMS mirror (12) with two axes corresponding to the first (14) and second axis (16) , is provided, and wherein a first actuator (18) oscillates the mirror (12) along the first axis (14) at the first deflection frequency, and a second actuator (20) also oscillates the mirror (12) along the second axis (16) the second deflection frequency oscillates, and wherein at least one further actuator (22) oscillates the first axis (14) and / or the second axis (16) at the modulation frequency. Method according to one of the Claims 1 to 8th , wherein the periodic deflection along the first axis (14) is provided by a first MEMS mirror (26) and the periodic deflection along the second axis (16) is provided by a second MEMS mirror (28), and wherein a first actuator is provided first mirror oscillates along the first axis (14) with the first deflection frequency and a second actuator oscillates the second mirror along the second axis with the second deflection frequency, and at least one further actuator at least one further mirror (30) with the modulation frequency along the first Axis (14) and / or the second axis (16) swings. Laser projection device (10) which is set up to carry out a method according to one of the preceding claims. Laser projection device (10) according to Claim 11 wherein the first actuator (18) comprises a piezo actuator and / or the second actuator (20) comprises a piezo actuator and / or the third actuator (22) comprises a piezo actuator. Laser projection device (10) according to Claim 12 , wherein the first actuator (18) as a piezo actuator comprises an electrostatic actuator, and / or the second actuator (20) as a piezo actuator comprises an electromagnetic actuator, and / or the third actuator (22) as a piezo actuator comprises an electrostatic one Actuator, includes. Vehicle with a laser projection device (10) according to one of the Claims 11 to 13th . Vehicle after Claim 14 wherein the laser projection device (10) is a head-up display projection device for projecting an image onto a windshield of the vehicle.

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